Not applicable.
The present invention is directed to medical catheters having improved mechanical properties.
Various types of materials are used for catheters, such as Dow Corning HP (high performance) or Dow Corning ETR (extra tear resistance) material. These types of materials have relatively high tear resistance. However, it would be desirable to have a catheter material that had a higher crush and creep resistance than Dow Corning HP or Dow Corning ETR.
Crush resistance and creep resistance are important properties for catheters because they can be subjected to various forces, such as compression and stretching forces after they are implanted within a patient. For example, a catheter that is implanted within a patient so that it can come into contact with the spinous processes can be frequently subjected to compression from the spinous processes.
Other materials have higher crush and creep resistance than Dow Corning HP and Dow Corning ETR. An example of such a material is Dow Corning MDX. While this type of material has relatively high crush and creep resistance, it is not considered to be suitable material for a catheter because a higher tear resistance material is believed to be necessary for such a catheter.
Tear resistance is important for catheters because they can be xe2x80x9cnickedxe2x80x9d or cut on the introducer needle during placement. Notably, this can occur without the physician implanting the catheter knowing that a nick or cut had occurred. Tear resistance is a mechanical property that indicates how quickly a cut or tear progresses to a fracture or break.
As it will be readily appreciated by those skilled in the art of medical catheters, certain mechanical properties, such as tear strength, abrasion resistance, resistance to shredding, compression set, crush and creep resistance are of great importance in the materials for any catheter device that is implanted into the human body. It should also be readily appreciated by those skilled in the art that catheters having improved mechanical properties, and particularly improved tear resistance, crush resistance and creep resistance provide higher performance and better results than catheters having lesser such mechanical properties.
The need still exists for catheters having improved mechanical properties, including improved tear resistance, crush resistance and creep resistance. The present invention provides such a catheter.
It is an object of the present invention to provide a catheter having improved overall mechanical properties over prior catheters.
It is another object of the present invention to provide tubular material for implantable medical catheters, which material has improved overall mechanical properties, including improved tear resistance, crush resistance and creep resistance.
The implantable medical catheter disclosed herein attains the foregoing and other objects of the present invention. More specifically, the implantable medical catheter of the present invention comprises a catheter defining at least one fluid passageway and a cured elastomer composition obtained by cross-linking an uncured blend composition that comprises an intimately admixed mixture that comprises the following components: (A) silica that had been silyliated by treatment and contains trialkylsilyl groups comprising approximately 23 to 45 percent by weight of the mixture; (B) a polysiloxane copolymer composed of divalent xe2x80x94R1R2SiOxe2x80x94, divalent xe2x80x94R3R4SiOxe2x80x94 and end-blocking R5R6R7SiOxe2x80x94 units, comprising approximately 55 to 77 percent by weight of the mixture, where R1 and R2 independently are lower alkyl of 1 to 6 carbons, phenyl or trifluoropropyl, R3 is vinyl, allyl, or other olefinic group having up to 4 carbons, R4 is lower alkyl of 1 to 6 carbons, phenyl or trifluoropropyl, and R5, R6, and R7 independently are lower alkyl of 1 to 6 carbons, phenyl, vinyl, allyl, or other olefinic group having up to 4 carbons and one double bond, the polysiloxane copolymer has a degree of polymerization (D.P.) approximately in the range of 3500 to 6500, and the olefin containing xe2x80x94R3R4SiOxe2x80x94 groups are present randomly distributed in the polysiloxane copolymer and approximately in the 0.05 to 0.3 mol percent range, with the provisos that when R1, or R2, or both represent phenyl groups then proportion of the phenyl-containing divalent siloxane units does not exceed 15 mol percent and when R1 or R2 or both represent trifluoropropyl groups, then the proportion of the trifluoropropyl-containing divalent siloxane units does not exceed approximately 40 mol percent in the polysiloxane copolymer; (C) a catalyst, and (D) an organohydrogen polysiloxane cross-linker, the catalyst and the cross-linker being present in the uncured blend composition in sufficient amount to cause the cross-linking reaction to occur.
In one embodiment, the polysiloxane copolymer, the xe2x80x94R1R2SiOxe2x80x94 group is xe2x80x94R(CH3)2SiOxe2x80x94, the xe2x80x94R3R4SiOxe2x80x94 group is xe2x80x94CH3(CH2xe2x95x90CH)SiOxe2x80x94, and the R5R6R7SiOxe2x80x94 group is xe2x80x94(CH3)2(CH2xe2x95x90CH)SiOxe2x80x94.
In one embodiment, the xe2x80x94CH3(CH2xe2x95x90CH)SiOxe2x80x94 group is present in the proportion of 0.142 mol percent in the polysiloxane copolymer.
In one embodiment, the silyliated silica includes trimethylsilyl groups in such quantity that the carbon content of the silyliated silica is in the range of approximately 4 to 8 percent by weight of the silyliated silica.
In one embodiment, the carbon content of the silyliated silica is approximately 7.3 percent by weight of the silyliated silica.
In one embodiment, the catheter includes barium sulfate (BaSO4).